csdiff: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/csdiff - from package: csdiff

You may install the required package with command yum install {package}

Error in other languages:
csdiff: bevel nie gevind nie
csdiff: comandă negăsită
csdiff: comando não encontrado
csdiff: commande introuvable
csdiff: command not found
csdiff: käsku ei ole
csdiff: không tìm thấy lệnh
csdiff: komanda nerasta
csdiff: Kommando nicht gefunden.
csdiff: kommandot finns inte
csdiff: komut yok
csdiff: nie znaleziono polecenia
csdiff: níor aimsíodh an t-ordú
csdiff: no se encontró la orden
csdiff: no s'ha trobat l'ordre
csdiff: opdracht niet gevonden
csdiff: parancs nem található
csdiff: perintah tidak ditemukan
csdiff: príkaz nenájdený
csdiff: příkaz nenalezen
csdiff: команда не найдена
csdiff: командата не е открита
csdiff: 命令找不到
csdiff: コマンドが見つかりません